In the picture you linked to, the microswitches only switch on the relays. The 70 amps required by the motors only flows through the relays, not the microswitches.

I would also recommend you ask about this circuit on a general eletronics forum or newsgroup where there are more Italian speakers. Were all happy to help but most of us here are limited to speaking English, and with these high currents it could be quite dangerous if a mistake in translation occurred. Please dont take this as an insult to your English skills, they are a lot better than my Italian